Portable data carriers (e.g., smart cards or chip cards) are known to include a plastic substrate within which a semiconductor device (i.e., integrated circuit--IC) is disposed for retaining digital data. This digital data may constitute program instructions, user information, or any combination thereof. Moreover, these smart cards are known to be operational in a contacted mode, whereby an array of contact points disposed on the plastic substrate and interconnected with the semiconductor device is used to exchange electrical signals between the smart card and an external card reader, or terminal. Similarly, there exists smart cards that operate in a contactless mode, whereby a radio frequency (RF) receiving circuit is employed to exchange data between the card and a card terminal. That is, the card need not come into physical contact with the card terminal in order to exchange data therewith, but rather must simply be placed within a predetermined range of the terminal.
Additionally, there exist smart cards that are alternatively operational in either a contacted mode or a contactless mode. Such cards are equipped with both RF receiving circuitry (for contactless operations) as well as an array of contact pads (for contacted operations). These cards are commonly referred to as combination smart cards, or combi-cards. It should be noted that in both the contacted smart card and the combi-card arrangements, the array of contact pads typically conform to the International Standard ISO 7816, which standard is incorporated herein by reference.
In practice, combi-cards are limited to use in either the contacted mode of operation or the contactless mode of operation. Accordingly, it is desirable to quickly and reliably determine which mode of operation is intended. Upon detection of the intended operating mode, the processing element (typically embodied in the semiconductor device) is able to correctly process the incoming and outgoing electrical signals.
One mode detection scheme is described in U.S. Pat. No. 5,206,495, issued on Apr. 27, 1993, and assigned to Angewandte Digital Elektronik (ADE). This reference describes a combi-card that includes a switching element device coupled between the semi-conductor device and the ISO Standard 7816 contacts and transmission coils. As described, the selection method includes a comparison of supply voltages received on the supply contact and the power received from the transmission coils. When a voltage is detected from the transmission coil, it is assumed that the contactless mode is intended, and the selection of contactless mode is made. While this arrangement may be suitable in some applications, it may be unreliable in an unstable RF environment (i.e., where stray RF signals are present). Moreover, this solution is not secure in the sense that it can easily be compromised by an unscrupulous user of the smart card.
Accordingly, there exists a need for a combination smart card that can reliably detect whether a contacted or contactless mode of operation is intended. Further, such a method that would provide a redundant check for added security would be an improvement over the prior art.